What is the role of FISH in HER2 breast cancer testing?

Updated: May 14, 2019
  • Author: Maurie Markman, MD, MS; Chief Editor: Karl S Roth, MD  more...
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Answer

Answer

FISH has been used to establish HER2 status when IHC yields equivocal results, but it is now also being used alone for this purpose in an increasing number of centers. The interpretation for HER2 FISH testing (HER2-to-CEP17 ratio and gene copy number) is as follows:

  • Positive HER2 amplification: FISH ratio higher than 2.2 or HER2 gene copy greater than 6.0.

  • Equivocal HER2 amplification: FISH ratio of 1.8-2.2 or HER2 gene copy of 4.0-6.0.

  • Negative HER2 amplification: FISH ratio lower than 1.8 or HER2 gene copy less than 4.0.


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